BUG: check_broadcast cannot return None

astropy/modeling/core.py

@@ -1061,11 +1061,12 @@ def _validate_input_shapes(self, inputs, argnames, model_set_axis):
                 )
             )
 
-        input_shape = check_broadcast(*all_shapes)
-        if input_shape is None:
+        try:
+            input_shape = check_broadcast(*all_shapes)
+        except IncompatibleShapeError as e:
             raise ValueError(
                 "All inputs must have identical shapes or must be scalars."
-            )
+            ) from e
 
         return input_shape
 

astropy/modeling/tests/test_core.py

@@ -11,7 +11,6 @@
 from numpy.testing import assert_allclose, assert_equal
 
 import astropy
-import astropy.modeling.core as core
 import astropy.units as u
 from astropy.convolution import convolve_models
 from astropy.modeling import models
@@ -984,40 +983,19 @@ def test__validate_input_shape():
 def test__validate_input_shapes():
     model = models.Gaussian1D()
     model._n_models = 2
-    inputs = [mk.MagicMock() for _ in range(3)]
-    argnames = mk.MagicMock()
-    model_set_axis = mk.MagicMock()
-    all_shapes = [mk.MagicMock() for _ in inputs]
 
-    # Successful validation
-    with mk.patch.object(
-        Model, "_validate_input_shape", autospec=True, side_effect=all_shapes
-    ) as mkValidate:
-        with mk.patch.object(core, "check_broadcast", autospec=True) as mkCheck:
-            assert mkCheck.return_value == model._validate_input_shapes(
-                inputs, argnames, model_set_axis
-            )
-            assert mkCheck.call_args_list == [mk.call(*all_shapes)]
-            assert mkValidate.call_args_list == [
-                mk.call(model, _input, idx, argnames, model_set_axis, True)
-                for idx, _input in enumerate(inputs)
-            ]
+    # Full success
+    inputs = [np.array([[1, 2], [3, 4]]), np.array([[5, 6], [7, 8]])]
+    assert (2, 2) == model._validate_input_shapes(inputs, model.inputs, 1)
 
     # Fail check_broadcast
     MESSAGE = r"All inputs must have identical shapes or must be scalars"
-    with mk.patch.object(
-        Model, "_validate_input_shape", autospec=True, side_effect=all_shapes
-    ) as mkValidate:
-        with mk.patch.object(
-            core, "check_broadcast", autospec=True, return_value=None
-        ) as mkCheck:
-            with pytest.raises(ValueError, match=MESSAGE):
-                model._validate_input_shapes(inputs, argnames, model_set_axis)
-            assert mkCheck.call_args_list == [mk.call(*all_shapes)]
-            assert mkValidate.call_args_list == [
-                mk.call(model, _input, idx, argnames, model_set_axis, True)
-                for idx, _input in enumerate(inputs)
-            ]
+
+    # Fails because the input shape of the second input has one more axis which
+    # for which the first input can be broadcasted to
+    inputs = [np.array([[1, 2], [3, 4]]), np.array([[5, 6], [7, 8], [9, 10]])]
+    with pytest.raises(ValueError, match=MESSAGE):
+        model._validate_input_shapes(inputs, model.inputs, 1)
 
 
 def test__remove_axes_from_shape():

astropy/modeling/tests/test_models.py

@@ -120,6 +120,14 @@ def test_inconsistent_input_shapes():
     y.shape = (1, 10)
     result = g(x, y)
     assert result.shape == (10, 10)
+    # incompatible shapes do _not_ work
+    g = Gaussian2D()
+    x = np.arange(-1.0, 1, 0.2)
+    y = np.arange(-1.0, 1, 0.1)
+    with pytest.raises(
+        ValueError, match="All inputs must have identical shapes or must be scalars"
+    ):
+        g(x, y)
 
 
 def test_custom_model_bounding_box():

docs/changes/modeling/15209.api.rst

@@ -0,0 +1,2 @@
+Creating a model instance with parameters that have incompatible shapes will
+now raise a ``ValueError`` rather than an ``IncompatibleShapeError``.